1. Field of the Invention
The present invention relates generally to filters for removing mercury vapor from the air and to the method of making same. More particularly, the invention relates to small annular-shaped filters for use in controlled atmosphere work enclosures of the type adapted to be used in dental operatories for mixing, mulling, cutting, and storing amalgam.
2. Discussion of the Prior Art
Mercury is used for a wide variety of industrial, chemical, medical, and dental purposes. Only recently, however, has the extreme danger of environmental contamination with mercury been realized. Mercury is a highly migratory, virulent poison that is readily absorbed by humans through the respiratory system, the gastrointestinal system and through unbroken skin. The maximum allowable concentration of mercury vapor in the air has been set at 50 micrograms per cubic meter. Since air saturated with mercury vapor at 20.degree. C contains a mercury concentration which exceeds the toxic limit by over 100 times, the critical hazards presented by mercury handling are at once apparent. Compounding the problem is the fact that in the human being mercury acts as a cumulative poison since only small amounts can be eliminated at a time by the human body.
Of particular concern are the hazards presented through careless handling of mercury in the dental office and dental operatory. In fact, the abnormally high rate of suicide among dentists is believed by many experts to be directly linked to mercury poisoning. Since the dental profession in the United States uses in excess of 200,000 pounds of mercury per year, or about four percent of the total amount used in the United States, a significant threat is presented, not only to the health of the dentist, but to his auxiliary personnel as well.
Environmental contamination through the use of mercury in dental operatories originates primarily from mercury spills and leakage or failure of mercury-containing capsules used in the trituration process. Additionally, mere excitation of any mercury contamination which may reside on the surfaces of the capsules or upon tools and equipment used in the operatory causes the mercury to vaporize and immediately spread throughout the adjacent areas. Also, contributing to the inordinately high level of mercury contamination found in dental offices and operatories is simple carelessness by the dentist and his assistants in the open air mulling, amalgam cutting, and mercury storage.
One of the most successful systems developed for use in handling mercury in dental and industrial operations is disclosed in pending application Ser. No. 779,013. The apparatus of this invention comprises a work station having a totally enclosed, controlled environment workspace wherein various mercury handling operations such as mixing, mulling, and amalgam cutting can be accomplished in absolute safety with no fear of personnel or atmospheric contamination. Mercury spills are completely contained within the unit and due to the novel design of the air-circulating system of the unit, a unique air flow pattern is continuously maintained within the enclosure to enable highly effective control of both vaporous and particulate mercury within the system. Although the filter of the present invention may be used in a wide variety of applications, it is ideally suited for use in work stations of the type described in Ser. No. 779,013. By placing the filter in the air outlet port of the unit, within the path of the air stream, all mercury contamination may be removed from the air prior to its emission into the atmosphere.
It is known in the art that iodized charcoals or charcoals prepared from coconut shells are capable of absorbing mercury vapor. In the past, therefore, various types of filters using such materials have been suggested. Typically, however, these filters have been designed for large scale industrial operations. The filters themselves, therefore, are generally quite large and bulky, often weighing several hundred pounds. With these filters, which are generally provided in the form of long tubular members filled with the charcoal, the air exhausted from the mercury handling area is passed through the length of the filter at very low velocity. Little, if any, work has been done in the past toward the development of a small, highly efficient filter such as that herein described for use with small mercury handling work enclosures. As will be appreciated from the description which follows, the filter of the present invention can be conveniently, replaceably mounted within the outlet port of a laboratory-type work enclosure. Due to its unique design, the filter can function in a highly efficient manner to remove mercury contaminants even from a relatively high velocity stream of air being emitted from the work enclosure. To applicant's knowledge, such a filter has not previously been developed.